The present invention is in the field of implantable medical devices and prostheses. More particularly, this invention is directed to devices useful as prosthetic ligaments and in vivo scaffolds for the regeneration of ligamentous tissue, and to methods of their fabrication and use.
Ligaments connect one bone to another usually where the bones form articulating joints in the human and animal species. The ligaments act in the joint as a mechanism for maintenance of joint stability, for guidance of joint motion, and for resistance to joint distraction forces. Without ligaments, the human and animal species would be unable to maintain the erect form. Injury to the ligaments results in either a normal physiological repair process, which can lead to resumption of normal joint mechanics, or to inadequate repair with loss of joint stability, abnormal joint motions, and occasionally to painful arthritis as a result of abnormal joint surface wear and tear. In general, ligaments that are outside of joints, and bathed in a rich vascular supply, have a good chance of healing normally after injury. Ligaments that are inside of joints, termed intra-articular ligaments, are generally bathed in synovial fluid, have a relatively poor blood supply, and heal poorly.
In the prior art, treatment of injured ligaments has generally been both by attempts to protect the ligament from further deforming stress and thereby to permit a normal physiological repair process to occur or to attempt a surgical repair with sutures, replacement, or excision (Johnson, R. J. et al. (1992) J. Bone Joint Surg. 74-A:140-151; Arnold et al. (1979) Am. J. Sports Med. 7:305; McDaniel et al. (1983) Clin. Orthop. 172:158; Rovere et al. (1983) Am. J. Sports Med. 104:205). With non-operative or operative repair, healing and regeneration of ligamentous tissue may occur. Generally, if the ligament is located intra-articularly, the repaired tissue is usually inferior to the original tissue and sometimes inadequate to withstand the normal joint forces. In view of the insufficiency of many primary repairs several previous attempts have been made to replace the ligamentous tissue with natural and artificial materials. Unfortunately, this also has resulted in significant problems related to those replacement materials.
In particular, replacement of ligaments in the prior art has been by autografting (Friedman et al. (1985) Clin. Orthop. 196:9), allografting (Webster (1983) Clin. Orthop. 181:238), xenografting (McMaster (1988) in "Prosthetic Ligament Reconstruction of the Knee" (Friedman and Ferkel, (eds.), W. B. Saunders, Philadelphia, pp. 96-100), or by using synthetic materials (Woods (1985) Orthop. Clin. North Am. 16:227). Autografting, or the substitution of the injured ligament with ones own tissue, is still the preferred modality (Amiel et al. (1986) Am. J. Sports Med. 14:449-462; Warren et al. (1990) AAOS 57th Annual Meeting, Anaheim, Calif, p. 84). Autografting alleviates the risk of transmission of diseases between donor and recipient, immunological complications, and complications from foreign body reactions. However, the weakening of the body part from which the substitution tissue is harvested, the extensive surgical procedures with both harvesting of the donor tissue and substituting the injured tissue, and the inadequate mechanical strength of the substituted tissues have prompted the search for alternative methods of repair.
Allografting, or the substitution of injured ligament with tissues from another person (either preserved live tissue or chemically processed tissue), has been practiced (Noyes et al. (1990) J. Bone Joint Surg. 72-A:1125-1136; Shine et al. (1990) Am. Sports Med. 18:457-465; Webster (1983) Clin. Orthop. 181:238; Bright et al. (1981) J. Pediatr. Orthop. 1:13). This approach has been only partially successful over the long term due primarily to the host's immunologic response to the graft, and to failures in the preservation and sterilization processes (Jackson et al. (1990) Am. J. Sports Med. 18:1-10; Minami et al. (1982) Hand 14:111). In addition, the risk of disease transmission is of particular concern for allografting (Prewett et al. (1991) Orthop. Res. Soc. 16:456).
Xenografting, or the substitution of the injured ligament with tissues from animal sources, has been tried. However, because of inadequate material processing leading to the presence of toxic and immunological substances in the graft, this method has met with minimal success (Teitge (1988) in The Crucial Ligament, (Feagin, ed.) New York, Churchill-Livingston, pp. 529-534).
Various synthetic polymers have been fabricated for ligament substitution, such as polypropylene, polyethylene terephthalate, carbon, polytetrafluroethylene (Claes et al. (1991) Orthop. Res. Soc. 16:598). Ligament substitution devices are intended to function as permanent implants, and thus are subjected to continuous intraarticular wear and tear. However, none of the present synthetic polymeric ligament devices has functioned successfully as a ligament substitute. Such devices have failed because of ligament rupture, joint particle reduction and resultant synovitis, abrasion of opposing joint surfaces, infection required extensive joint debridement and ligament removal, persistent effusion, and bony tunnel widening (Woods et al. (1991) Am. J. Sports Med. 19:48-55; Woods (1985) Orthop. Clin. North Am. 16:227). Thus, artificial materials are generally insufficiently durable or mechanically compatible to tolerate the repetitive joint loading, and have never been demonstrated to restore normal joint mechanics.
The concept of a resorbable template or scaffold for tissue repair and regeneration has received rigorous attention in recent years. Repair of tissues such as skin, nerve, and meniscus has been attempted using both the synthetic and natural resorbable polymers. For example, Yannas et al. (U.S. Pat. No. 4,060,081) fashioned endodermal implants out of glycosaminoglycans and natural collagen. Nyiles et al. (Trans. Am. Soc. Artif. Intern. Organs (1983) 29:307-312) reported the use of synthetic resorbable polyesters for peripheral nerve regeneration applications. Li (U.S. Pat. No. 4,963,146) used a porous, semipermeable, resorbable collagen conduit as a scaffold for nerve regeneration.
However, even with the foregoing technologies, which have been applied to the reconstruction of anatomical structures, a structure successful as a prosthetic ligament and constructed from totally resorbable materials, or analogs thereof, has not yet been developed. Therefore, what is needed is a prosthetic ligament including a scaffold composed of biocompatible materials which is soft, strong, resorbable, and which can support ligamentous growth.
Accordingly, it is an object of this invention to provide a ligament replacement or prosthesis which is biomechanically able to withstand normal joint forces and is able to function at those loads to protect the surrounding cartilage.
Another object is to provide a ligament replacement or prosthesis which is biomechanically able to provide joint stability.
Yet another object is to provide a resorbable prosthesis which acts as temporary in vivo scaffold for ligament fibroblast infiltration and ligament regeneration.
A further object is to provide a method for insertion and fixation of a ligament prosthesis.
Another object is to provide a method of regenerating ligamentous tissue in vivo.
Still a further object is to provide a method by which such prosthetic ligament can be fabricated.